An assessment of the relationship between corticosteroid treatment and changes in bone density and growth in children receiving long-term oral corticosteroids (any of the various adrenal-cortex steroids). The subjects of this study will be children four to sixteen years old, receiving long-term corticosteroids or initiating long-term corticosteroid treatment. Children receiving growth hormone, a bisphosphonate, calcitonin, or birth control will be entered into the longitudinal database, but will be analyzed separately. It is unclear whether all children receiving long-term inhaled or oral corticosteroidal treatment should be targeted for interventions to prevent loss of bone density, or if preventative treatments should be limited to those children at high risk due to the dose or duration of corticosteroidal use or other factors that influence the loss and recovery of bone mass. Subjects will be entered into this longitudinal study monitoring changes in growth and bone density over time. Because corticosteroids interfere with the absorption of calcium, all children will receive advice about dietary calcium intake and calcium supplements. Data collection will include height, weight, race, gender, activity level, functional status, dietary calcium and vitamin D, Tanner stage, and medication use. Bone mineral density will be measured at the AP spine every six months, and the femur and the whole body, yearly, using dual-energy x-ray absorptiometry, semiannually. Biochemical measurements of bone turnover will be made at the same time. Final analysis will be derived from the relationship between corticosteroid treatment (dose, duration, schedule) and change in lumbar spine, femoral neck, and total body bone mineral density (BMD) in children. Also, the relationship between corticosteroid treatment and change in height and weight, changes in rate of growth, changes in markers of bone formation and resorption, changes in ILGF-1, LH FSH, estrogen, and testosterone levels will be determined. Lastly, changes in bone density, height, weight, markers of bone turnover, and growth will be observed after withdrawal of corticosteroid treatment.